The invention concerns polyurethanes prepared through the use of cyclohexane-1,4-diisocyanate with a high content of the trans-isomer as well as methods for their preparation and use.
Polyurethanes have been recognized for a long time as highly useful substances in the manufacture of fibers and films as well as in the production of molded bodies; their suitability for use in impregnation and in coating treatments is also well-known in the art. The preparation of polyurethanes in general involves the reaction of polymers bearing terminal hydroxyl groups, e.g., polyethers, polyesters, polyacetals, polylactones, polycarbonates, etc., either alone or in admixture with chain extenders, with polyisocyanates, in particular diisocyanates. Methods for carrying out these reactions have been detailed in numerous scientific publications and patent specifications.
Although a large number of polyurethanes and methods for their preparation are known, a tremendous amount of research is still directed to the investigation of novel compositions with properties more advantageous for the myriad of uses which might be envisaged, as well as to methods for the preparation thereof.
Polyurethanes prepared through the use of cyclohexane-diisocyanate are known. Thus, the German DT-OS No. 1,955,725 describes such polyurethanes and methods for their preparation. However, the cyclohexane-1,4-diisocyanate employed therein contains at most 85.5% of the trans-isomer, and so the thus-prepared compounds do not exhibit the advantageous properties of the compounds of the instant invention.
The preparation of polyurethanes using the trans-isomer of cyclohexane-1,4-diisocyanate in practically pure form has been described by A. G. Kozhevov and co-workers in Vyskomol, soyed A14 Nr. 3, 662-668 (1972). The primary focus of this scientific article is the kinetic behavior of the corresponding mono- and diisocyanates with respect to reaction with alcohols; the polyurethane products of the therein-described reaction of trans-cyclohexane-1,4-diisocyanate and 1,4-butanediol are of virtually no technological value, as they are of a comparatively low molecular weight and are readily soluble in many customary solvents such as acetone and methanol. They are thus totally unsuitable for use in e.g., the manufacture of molded bodies.